Electromagnetic Induction: Faraday's Law, Lenz's Rule and Eddy Fields
How a changing magnetic field creates electricity — the principle behind every generator
Big Idea: A magnet at rest near a coil does nothing. But the moment the magnetic flux through the coil changes — because the magnet moves, the field strengthens, or the coil turns — an electromotive force (EMF) appears and drives a current. This single fact, discovered by Michael Faraday in 1831, is how the generators at the Toktogul hydro-electric station, every bicycle dynamo and every transformer turn motion into electric energy.
By the end of this topic you will be able to:
- define magnetic flux and compute it from B, area and angle;
- state and apply Faraday's law of electromagnetic induction, ε = −N ΔΦ/Δt;
- use Lenz's rule to find the direction of an induced current;
- calculate the motional EMF of a conductor moving through a field, ε = Blv;
- explain what an eddy (vortex) electric field is and why it can drive a current in a conductor that never moves.